Servo systems in optical data recording devices such as optical tape drives utilize tracking error signals, detected from the optical media via an optical pickup unit (OPU) device, to accurately record and then retrieve data on the optical media.
FIGS. 1 and 2 illustrate a portion of a typical optical recording medium. FIG. 1 is a top view while FIG. 2 is a side view. Optical data storage medium 10 includes a nanostructure surface relief pattern embossed on the surface of the optical medium. The nanostructure includes lands 12 and grooves 14 embossed in the Z direction (i.e., parallel to the face of optical data storage medium 10) thereon in a performing process. These surface relief patterns are used to generate the tracking signals used by a servo system to track the position of an optical head reading or writing to the medium. An optical drive OPU with the aid of electronic signal processing generates a tracking error signal (TES) from the detected patterns. In order to establish an addressing capability for these recording tracks, the edges of these embossed lands 12 and grooves 14 relief patterns are structurally modulated in the horizontal directions parallel to the face of optical recording data storage 10 (e.g., Y axes to track X axes) with sinusoidal patterns 16 (i.e., wobbles) which contain individual track address codes. These wobble patterns embedded (or embossed) on the surface of optical data storage media such as optical tape, during media pre-formatting process, and thereafter detected by the optical read element during normal operation of the data storage devices are the essential part of reliable data recording and retrieval functionality of the these devices. FIG. 1 also depicts recording marks 18 encoded thereon.
A technique referred to as “Radial Push Pull” Tracking signal generation (also referred to as “Main Push Pull” (MPP)), have been conventionally used to generate the Tracking Error Signal (TES) for the rewritable optical recording media preformatted with “land” and “groove” track geometries as set forth above. This scheme generates a reference tracking signal based on the geometries of land and grooved tracks on the media and detectable by a main quad photodetector (QPD) of the OPU. FIG. 3 provides a schematic illustration of a typical signal processing scheme for the TES signal generated by the QPD. Signal processing system 20 includes recording/reading head 21. Recording/reading head 21 includes quad photodetector 22 which includes individual photodetectors 24, 26, 28, and 30. Signals 32, 34, 36, 38 from photodetectors 24, 26, 28, 30 are amplified by amplifiers 42, 44, 46, 48 to provide signals 52, 54, 56, 58. Signals 52, 54 are provided to adder 60 which outputs summed signal 62. Signals 56, 58 are provided to adder 64 which outputs summed signal 66. Summed signal 62 and summed signal 66 are inputted into subtractor circuit 70 with outputs difference signal 72 which is further processed to provide TES signal 78 and wobble signal 80. For example, low pass filter 82 receives difference signal 72 as an input and outputs TES signal 78 while band pass filter 84 receives difference signal 72 and outputs wobble signal 80. The high frequency wobble signal includes, among other information, the key data track ID and Address codes. Moreover, TES signal 78 and wobble signal 80 are used by recording/reading head servo system 86 to provide positioning information regarding the position of head 21. In particular, digital servo systems control the dynamic operation of the OPUs by using wobble signal information to place the OPU on the correct desired data track. Additional methods for detecting wobble signals and/or Tracking Error Signals are set forth in U.S. Pat. Nos. 5,383,169; 6,009,059; and 6,937,542; the entire disclosures of which are hereby incorporated by reference.
In the current optical tape methodologies, the multiple OPUs with multiple data recording zones on the media are utilized. In such systems, many analog-to-digital converters (ADC's) are needed to digitize the multiple wobble signals from multiple recording zones to be used by system Digital Signals Processors. Since there are significant number of wobble signals present in such system, the excessive cost, space utilization, power consumption, and high number of inputs and output associated with the requisite numerous ADCs pose a serious produced feasibility problem
Accordingly, there is a need for improved methods of digitizing wobble signal in optical data storage systems.